Technical Abstract:
Over 1.5 billion gallons of ethanol are produced annually in the U.S., of which 95% was derived from fermentation of corn starch. Demand for ethanol, as a substitute for gasoline, is expected to increase because of concerns related to national security, economic stability, environmental impact, and global warming. Expanding fuel ethanol production will require developing alternate low cost feedstocks available in sufficient quantities to substitute for starch. Corn fiber, a low value co-product generated during wet milling, is a promising potential feedstock because it is centrally stockpiled, low in naturally occurring inhibitors, and contains over 50% w/w non-cellulosic carbohydrates. We are developing a process for conversion of corn fiber into ethanol. In the first step, the non-cellulosic carbohydrates are hydrolyzed into monomers using a pilot scale jet syphon batch reactor. Sulfuric acid is used as a catalyst, and direct steam is used to heat the slurry to 140-145 deg C. Following treatment, the hydrolysate is neutralized with calcium hydroxide. The final product contains a mixture of arabinose, glucose, and xylose with a total sugar concentration of approximately 8% w/v. Yeast typically used for fermentation of starch streams (e.g., Saccharomyces cerevisiae) cannot ferment the pentoses present in corn fiber hydrolysate. Therefore, recombinant ethanologenic Escherichia coli strain K011 was used for the fermentations. Ethanol fermentations have been carried out with up to 20 L of corn fiber hydrolysate.